Method of and apparatus for signal reproduction



June 25, 1963 J. s. wHnEFoRD 3,095,482

METHOD OF AND APPARATUS FOR SIGNAL REPRODUCTION Filed May 8, 1959 IIIIIIIIIIIIIIIIIIIIIIIIII O QNYFI IN V EN TOR. M5550# 5. Wef/ff/-a BY Arme/vf V5 Ir Ir United States Patent 3,095,482 METHOD OF AND APPARATUS FOR SIGNAL REPRODUCTION Joseph S. Whiteford, Seabrook, N .H. Filed May 8, 1959, Ser. No. 811,937 18 Claims. (Cl. 179100.2)

The present invention relates to methods of and apparatus for signal reproduction and, more particularly, to the reproduction of sound signals.

It has heretofore been proposed to simulate desirable sound reverberation characteristics produced in a coniined space, such as a large church or the like, by locating in a room, building or other space that does not have such desired reverberation characteristics, a plurality of loudspeakers at successive positions along the walls of the room, building or other space, corresponding in positional sequence to the time sequence of operation of a corresponding plurality of successively operated sound reproducing transducers, energized successively from a source of sound signals and connected With the corresponding loudspeakers. The sound is thus caused to be fed successively to the successively positioned loudspeakers, Say, from the front to the back of the room, building or other space, thereby simulating the actual travel of sound Waves from the front to the back. By controlling the level of the sound energy emanating from each loudspeaker, a somewhat realistic sound-decay pattern can be obtained which, when supplemented by a signal fed back from the last of the plurality of reproducing transducers to the source, in a carefully controlled manner, can effect an over-all simulated reverberation time that corresponds to the desired reverberation time.

The reverberation produced by this kind of device consists of a series of segments, comparable to pulses or discrete echoes, the duration of which is equal to the time between successive energizations of the successive reproducing transducers. VIn the case of a magnetic tape source of signals, With a plurality of substantially equally spaced playback-head transducers, this duration Would correspond to the time that it takes any given point on the tape to travel from one head to the next. The successful operation of the system, however, depends upon keepingV this time duration short enough; and this can be accomplished by close head-spacing and high tape-speed. Unfortunately, there are several very severe limitations irnposed upon the application of these techniques. In a particular installation, for example, a time duration of a tenth of a second has been found to be sucient for organ music and choral singing. When more explosive sounds with sharp transients are involved, such as, for example, cymbal clashes in orchestral music,a much shorter time would be required in order to mask the discrete-pulse effect inherent in the system. Since Whatever natural reverberation that may exist in the room, building or other space assists in this masking, the maximum permissible pulse-time length has to be, in the last analysis, decided by test for any given room, building or other space, taking into account the types of sounds that are to be reverberated.

Another audible, regularly recurring, undulating pulsation inherent in a system of this kind is what may be termed pumping It occurs each time any given signal re-enters vthe recording head via the feedback-path from the last reproducing playback head, and is, therefore, in time, equal to the short pulse time described above multiplied by the number of playback heads. In the case of six playback heads, for example, and the onetenth second time duration, this would be six-tenths of a second. This disturbance can be minimized by Very1 careful adjustment of all level controls, so that the over- 'ice all signal decay is kept as linear as possible. The only way completely to eliminate this diculty, however, would be to use no feedback at all and, consequently, a sufliciently large number of playback heads to obtain the required reverberation time. This is, in most instances, impractical cost-wise, but can be approached by the use of as many playback channels as possible with consequently as little feedback as possible. Such design, furthermore, assists in obtaining good linearity from the system, a prime requirement for long reverberation time.

In simulated reverberation systems of the prior art, the principal disadvantages are at least two-fold.

First, since the pulses or echoes are being reproduced by pairs of loudspeakers operative in numerical sequence with the reproducing playback channels, from the front toward the rear, as before described, the feeding-back of the signal from the last playback head to the recording head, causes the sound suddenly to jump toward the front, again, and then to travel the same path from front to back, once more. Because the sound does this several times over before it dies out, it can readily be seen that the only acoustical dimension that the room, building or other space thus acquires is that of length. 'It appears to have no breadth and very little height, in spite of the fact that the loudspeakers may be placed well above earlevel. All the echoes seem to converge upon the rear and, every time they get there, one completely loses track of them because they suddenly jump toward the front again. The result is an illusion of a sound-pile created by an immense reilecting rear Wall. sion that all the reverberation comes from there and almost from nowhere else.

Secondly, the pumping effect, before described, demands very linear adjustment of the overall reverberation decay, frequency-response-Wise as well as level-Wise. Un-V fortunately, this is not the Way reverberation occurs in an actual pleasingly reverberant building, where the low frequencies are usually absorbed far less rapidly than the high frequencies, and where this unevenness of absorption is even more pronounced as the distance from the sound source increases.

An object of the present invention, accordingly, is to provide a new and improved method of and apparatus for sound reproduction of the character described that shall not be subject to any of the above-mentioned disadvantages; but that shall, to the contrary, add breadth and height to the reverberation illusion andsubstantially eliminate the pumping and piling effects.

A further object is to provide a novel sound-reproducing apparatus of more general utility, as well.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing, the single FIGURE of which is a combined block-and-schematic circuit diagram illustrating the invention in preferred form.

For purposes of illustration, the invention .is shown applied to a church or `similar auditorium 1 having organ pipes at the front, operated from la console 3, and in which it is desired to simulate fthe acoustic response of a much larger building, :orf one with less acousv `One has the impresare disposed .at successively positioned lintervals, from front to back, along the oppositely disposed side walls f the church or auditorium 1, as previously discussed, and a further'pair of speakers l2 12 is provided at the back. Again, however, it `is to be understood that more or less speakers may be employed, las desired. Each of the pairs of loudspeakers ris energized to produce an audible indication of the signal from a' corresponding .sound playbackhead or pick-up transducer, as of the magnetic type, .associated with a magnetic tape S passed between a takeeoff reel 7 and la `talee-up reel 9. Conventional erase heads 11, `as .of the permanent magnet and attenuating-currcnt types, may insure that .the tape is free `of residual signals before reach-ing the recording head `13. The recording head 13 lis .energized through a mixer Kand recording amplifier system 15, connected by conductor paths 25 and 25 to the respective pair of microphones 23 and 23', in turn disposed to receive the music from the organ pipes. The

' recorded tape 5 .then proceeds successively past the successively disposed play-back heads 2t), 40, 60, 8G, 100, 120, each positoned therealong at substantially equal intervals, preferably substantially the same as the 'distance between the recording head 13 and the first playback head 20, as shown.

The successively energized playback heads Ztl, 40, 60, 80, 160 land 120, will thus transmit signals through corresponding pre-amplilier channels 22, 24, 26, 28, 30 and 32, having conventional level, bass and treble controls, by Way of corresponding conductor paths `42, 44,v 46, 48, 50 and 52, to corresponding further amplifier stages 2.2', 24', 26', 28', 30 and 32', thereby successively to energize the pairs fof loudspeakers 2 2', 4 4', 6 6', 8 8', 1t} and 12 12', respectively connected thereto.

While creating the illusion of space, when adding reverberation to music, is natural and therefore desirable, this spfaceaillusion should not .a-ll occur in one direction only, .as in the lengthwise direction before discussed. It should also add breadth yand height. In a real building, of course, an infinity of reflections strikes the listeners ears from all directions so that the reverberation is not confined to sound waves shuttling back and forth between front vand back. There is, however, some feeling of sound-travel from front -to back in a building 'which is .spacious and, more specifically, oblong. LFor reason, for a given building of this basic general shape, one is well advised to retain, therefore, the `fundamental concept of connecting the channels sequentially.

yIn accordance with the present invention, accordingly,

simulated secondary, random reflections are created,

emanating from the loud-speakers of properly chosen channels at proper times, in addition to the primary scheme of sequential echoes, thereby creating the illusion of a three-dimensional reverberant space.

To achieve this effect, it has been found necessary to observe the following requirements.

First, ythere must be sufficient randomness in the simulated secondary reflections. It is advisable, `for instance, to :avoid insofar las possible, simulating :a secondary reflection of .a signal from one channel in `an adjacent channel. Secondly, the levels of these simulated reflections must be carefully determined and, more .often than not, their overall level should be kept slightly below that of the primary scheme. If thus properly adjusted, these simulated secondary reflections have been found to add such a feeling of realism to the overall reverberation, that frequency response corrections may be introduced to a large extent Iwithout inducing .any consciousness of pumping or piling in the listener.

To .attain this end, the preemplier 22, yassocia-ted with the first-channel playback head 20 .and the vfirst pair of loudspeakers 2 2' .is shown feeding pant of its primary signal output through a level control, schematically illustrated as a variable resistor R2, to the pre-amplifier stage 23 of the fourth channel associated with the fourth pair of loudspeakers 8 8'. Similarly, the second-channel preamplifier 24 is connected by R4 to the f-thecliannel preamplifier 30 associated with the fifth pair of loudspeakers 1tl 10'. Other randomly selected interconnections of `channels are :effected by R12, between the sixth channel associated with loudspeakers yl2 12 and the first channel; by Rm, between the fifth channel asso ciated with the fifth pair of loudspeakers ih ltl yand the third channel associated with the third pair of loudspeakers 6 6'; by R8 between the fourth and sixth channels; and by R6 between the third and second channels.

A part of the primary signals reproduced iat the successively operated pairs of speakers will thus be reproduced yas seco-ndary signal-s .at other randomly selected speakers, simulating random reflections thereof and' giving the illusion of .three-dimensional reverberation, as above discussed. 'In order to produce the desired effect, moreover, :it has been found that .the level of the part of the primary signal thus fed from `one speaker channel to another speaker channel should be adjusted tto the same level `as .the primary signal of the said one speaker channel from which it originates. In some cases, this level of :the secondary signal may be reduced by any required reduction constant representative of thelamount, if any, by which the secondary or simulated reflection signal, should be lower in level than the primary sign-als of the loudspeakers.

As an illustration, in a small church about eighty feet in length, the successive pairs of speakers were spaced at ten-foot intervals. The `actual sound-wave travel time for this spacing was approximately 0.01 second. By employing a tape speed and playback head spacing such as to produce a simulated travel time (between energization of successive pairs of speakers) of about 0.1 second, the apparent length of the church was increased by a factor of ten. The following chart illustrates the selected primary signal levels for the six channels, corresponding to the successive pairs of speakers 2 2', 4 4', 6 6',V

8 8', 1ll 10' 1:2 12; the random interconnection of channels as previously described; and the adjusted levels of the parts of the primary signals fed by such interconnections to serve as secondary signals at other channel speakers, thus to simulate random reflections. The reverberation .time desired was about two and a half seconds.

Secondary Secondary Secondary signal, Primary signal signal using Channel signal level originates level unreduction- (decibels) from reduced constant of channel (decibels) 3 decibels ldown (decibels) -In accordance with an additional feature of the present invention, compensation is effected for the previously mentioned phenomenon that the decrease in level at the speakers, successively more distant from Vthe front, is

less for the low sound frequencies than for the high l sound frequencies. By adjusting the frequency response of the successive pre-amplifiers so that the bass is boosted and the treble attenuated more and more in the successive channels frorn front to back, the required less reverberation of the high frequencies can be attained. Feedback from the last channel pre-amplifier 32 to the recording amplifier 15 will then be adjusted by frequencyresponse and level controls so that a greater level of lows than highs is fed back, and a smooth reverberation decay is obtained.

It will be clear that any other type of storage or other signal-reproducing system than the magnetic type may be employed, and that, indeed, the techniques of the invention may be used with other kinds of signals than audible sound signals, wherever the results attainable by the invention are desired.

Instead of recording live sounds, moreover, one could inject recorded or stored sound signals into a first playback head replacing the recording head 13, preferably employing a relatively large number of successive playback heads 20, 40, `60, etc. to avoid the necessity for the before-described feedback. The recorded or stored sounds need not be stored on magnetic tape, since phonograph records, optically or photographically recorded films, or other kinds of record media may also be employed.

Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. Sound-reproducing apparatus having, in combination, a plurality of time-sequentially operative soundreproducing channels, a plurality of loud-speakers distributed in positional sequence corresponding to the time sequence of the operation of the reproducing channels, each loud-speaker corresponding to and being connected with the corresponding reproducing channel, means for pre-adjusting the level of each sound-reproducing channel to successively lower predetermined values to correspond to the successive positional separations of the loudspeakers, a plurality of further connections disposed between each channel and one or more randomly selected noncorresponding loudspeakers, and means for adjusting the level of signal fed along each further connection from each channel to a randomly selected non-corresponding loudspeaker to a value corresponding to the said preadjusted level of that channel.

2. Sound-reproducing apparatus as claimed in claim l and in which the said value corresponding to the said pre-adjusted level is substantially equal to the said preadjusted level less a predetermined constant value.

3. Signal-reproducing apparatus having, in combination, a plurality of time-sequentially operative signalreproducing channels, a plurality of signal indicators distributed in positional sequence corresponding to the time sequence of the operation of the reproducing channels, each indicator corresponding to and being connected with the corresponding reproducing channel, means for pre-adjusting the level of each signal-reproducing channel to successively different predetermined values to correspond to the successive positional separations of lthe indicators, a plurality of further connections disposed between each channel and one or more randomly selected non-corresponding indicators, and means for adjusting the level of signal fed along each further connection from each channel to a randomly selected non-corre sponding indicator to a value corresponding to the said pre-adjusted level of that channel.

4. Sound-reproducing apparatus having, in combination, a source of sound signals, a plurality of pick-up devices for responding to the signals and each connected to a sound-reproducing channel, means for rendering the successive pick-up devices time-sequentially operative to respond to the source of sound signal-s, thereby successively to energize the corresponding sound-reproducing channels, a plurality of loudspeakers distributed in positional sequence corresponding to the time sequence of the operation of the pick-up devices, each loudspeaker corresponding to and being connected with the corresponding sound-reproducing channel, means for pre-ad justing the level of each sound-reproducing channel to succesively lower predetermined values to correspond to the successive positional separations of the loudspeakers, a plurality of further connections disposed between each channel and one or more randomly selected non-corresponding loudspeakers, and means for adjusting the level of signal fed along each further connection from each channel to a randomly selected non-corresponding 6 loudspeaker to -a value corresponding to the said preadjusted level of that channel.

5. Sound-reproducing apparatus as claimed in claim 4 and in which the source of sound signals comprises a magnetic medium traversing a predetermined path and the pick-up devices comprise playback transducers substantially equally spaced a predetermined distance from one another along the path of the medium.

6. Sound-reproducing apparatus as claimed in claim 5 and in which a recording channel is provided with recording transducer means for storing sound signals upon the magnetic medium, the recording transducer means being spaced substantially the said predetermined distance from the rst of the plurality of playback transducers.

7. Sound-reproducing apparatus as claimed in claim 6 and in which the levels of the low-frequency components of the signals in the channels are accentuated relative to the high-frequency components.

8. Sound-reproducing apparatus as claimed invclaim 6 and in which feedback means is provided between one or more of the channels and the recording transducer means, having control means for feeding back a greater level of low than high-frequency sound components of the sound signals.

9. Sound-reproducing apparatus as claimed in claim 6 and in which six channels are provided having substantially the following primary signal levels at the corresponding loudspeakers and secondary signal levels at the' said non-corresponding loud-speakers, with the following said further connections therebetween:

Channel Primary from which Secondary Channel signal level Further consignal level (decibels) neetion is (decibels) eieeted l0. Sound-reproducing apparatus having, in combination, a source of sound signals, a plurality of pick-up devices for responding to the signals and each connected to a sound-reproducing channel, means for rendering the successive pick-up devices time-sequentially operative to respond to the source of sound signals, thereby successively to energize the corresponding sound-reproducing channels, a plurality of loudspeakers distributed in positional sequence corresponding to the time sequence of the operaltion of the pick-up devices, each loudspeaker corresponding to and being connected with the corresponding soundreproducing channel, and a plurality of further connections, one disposed between each channel and one or more non-adjacent and randomly selected non-corresponding loudspeaker, said source of sound signals comprising a magnetic medium traversing a predetermined path and the pick-up devices comprising playback transducers substantially equally spaced a predetermined distance from one another along the path of the medium, said apparatus having a recording channel provided with recording transducer means for storing sound signals upon the magnetic medium, the recording transducer means being spaced substantially the said predetermined distance from the iirst of the plurality of playback transducers, and said apparatus having feedback means between at least one of the channels and the recording transducer means with control means for feeding back a different level of low than highfrequency sound components of lthe sound signals.

l1. Sound-reproducing apparatus having, in combination, a source of sound signals, a plurality of pick-up devices for responding to the signals and each connected to a sound-reproducing channel, means for rendering the successive pick-up devices time-sequentially operative to reannalisa spond to the source of sound signals, thereby successively to energize the corresponding sound-reproducing channels, a plurality of loudspeakers distributed in positional sequence corresponding to the time sequence of .the operation of the pick-up devices, each loudspeaker corresponding to and being connected with the corresponding soundreproducing channel, and a plurality of further connections, one disposed between each channel and one or more non-adjacent and randomly selected non-corresponding loudspeaker, said further connections being provided with means for adjusting .the level of signal fed therealong.

12. Sound-reproducing apparatus having, in combination, a group of time-sequentially operative sound-reproducing channels, a group of loudspeakers distributed in positional sequence corresponding to the time sequence of the operation of the reproducing channels, each loudspeaker corresponding to and being connected with the corresponding reproducing channel, and a further connection between each of a plurality of said channels and a non-corresponding loudspeaker that is connected to an other channel not immediately adjacent thereto, each of said plurality of channels being unconnected to immediately adjacent channels.

13. The apparatus of claim 12, wherein each of said sound-reproducing channels has a sound pick-up head providing signals to be reproduced.

14. The apparatus of claim 12, each of said soundreproducing channels having a sound pick-up device, said apparatus having a source of sound signals and said channels being rendered time-sequentially operative by means for causing said pick-up devices to respond to said source of sound signals in time sequence.

l5. The apparatus of claim 14, each of said channels having an amplifying means connecting its pick-up device to its loudspeaker, the amplifying means of each of said other, nonadjacent, channels having means for mixing the signals from its pick-up device and from the fur-ther connection to that channel.

16. The apparatus of claim 14, said source of sound signals comprising a magneticfmedium traversing a predetermined path, and the pick-up devices comprising playback transducers substantially equally spaced a predetermined distance from one another along the path of the medium.

17. The apparatus of claim 16, said apparatus having a recording channel provided with recording transducer means for storing sound signals upon the magnetic medium, the recording transducer means being spaced substantially the said predetermined distance from the iirst of the plurality of playback transducers.

18. Signal-reproducing apparatus having, in combination, a group of time-sequentially operative signal-reproducing channels, a group of signal indicators distributed in positional sequence corresponding to the time sequence of the operation of the reproducing channels, each indicator corresponding to and being connected with the coresponding reproducing channel, and a further connection between each of a plurality of said channels and a non-corresponding indicator that is connected to another channel not immediately adjacent thereto, each of said plurality of channels being unconnected to immediately adjacent channels.

References Cited in the file of this patent UNITED STATES PATENTS 2,279,018 Wolfe Apr.V 7, 1942 2,298,618 Garity et al. Oct. 13, y1942 2,327,956 Begun Aug. 24, 1943 2,931,862 Vermeulen et al Apr. 5, 1960 FOREIGN PATENTS 1,033,682 France July 15, 1953 209,781 Australia Aug. 14, 1957 

1. SOUND-REPRODUCING APPARATUS HAVING, IN COMBINATION, A PLURALITY OF TIME-SEQUENTIALLY OPERATIVE SOUNDREPRODUCING CHANNELS, A PLURALITY OF LOUD-SPEAKERS DISTRIBUTED IN POSITIONAL SEQUENCE CORRESPONDING TO THE TIME SEQUENCE OF THE OPERATION OF THE REPRODUCING CHANNELS, EACH LOUD-SPEAKER CORRESPONDING TO AND BEING CONNECTED WITH THE CORRESPONDING REPRODUCING CHANNEL, MEANS FOR PRE-ADJUSTING THE LEVEL OF EACH SOUND-REPRODUCING CHANNEL TO SUCCESSIVELY LOWER PREDETERMINED VALUES TO CORRESPOND TO THE SUCCESSIVE POSITIONAL SEPARATIONS OF THE LOUDSPEAKERS, A PLURALITY OF FURTHER CONNECTIONS DISPOSED BETWEEN EACH CHANNEL AND ONE OR MORE RANDOMLY SELECTED NONCORRESPONDING LOUDSPEAKERS, AND MEANS FOR ADJUSTING THE LEVEL OF SIGNAL FED ALONG EACH FURTHER CONNECTION FROM 